Demystifying the init system (PID 1)

This is an interesting Linux init example with proof of concept code written in Ruby.

Felipe Contreras

With all the talk about debian choosing a default init system (link, link), I’ve decided to share with the world a little project I’ve been working on to help me understand /sbin/init aka. PID 1.

In this blog post I will go step by step showing what an init system must do to be functional. I will ignore all the legacy SysVinit stuff, and technical nuances, and just concentrate on what’s really important.

Introduction

First of all, what is ‘init‘? In it’s essence it’s a process that must be running at all times, if this process ends, the kernel enters into a panic mode, after which you cannot do anything else, except rebooting.

This process doesn’t need to do anything special, you can use /bin/sh as your init, or even /bin/yes (although the latter wouldn’t be very useful).

So let’s write our very first init.

View original post 2,297 more words

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